DNSCrypt

DNSCrypt offers a way to protect clients against attacks related to the modification and manipulation of DNS traffic — The main objective of DNSCrypt is authentication of the communication channel between the client (you) and a resolver supporting the protocol — This will protect the client from man in the middle attacks. In addition, encryption of DNS communication improves the client's privacy. DNSCrypt is the client-side version of dnscrypt-wrapper.

DNSCrypt verifies that responses you get from a DNS provider have been actually sent by that provider, and haven't been tampered with.

This is not a VPN. It doesn't mask your IP address, and if you are using it with a public DNS service, be aware that it will (and has to) decrypt your queries.

If you are using it for privacy, it might do the opposite of what you are trying to achieve. If you are using it to prevent VPN "leaks", this isn't the right tool either: the proper way to prevent VPN "leaks" is to avoid sending data to yet another third party: use a VPN service that operates its own DNS resolvers.

Installation

dnscrypt-proxy and libsodium is in the official repository for Chaos Calmer 15.05 and up.

opkg update
opkg install dnscrypt-proxy

If installed skip to configuration.

If somehow you can't install it that way, proceed with the following instructions.

Configuration

DNSCrypt is listening on address and port: 127.0.0.1:5353. We need to set OpenWrt to send DNS request to that address.

Server configuration

dnscrypt-proxy

The config file /etc/config/dnscrypt-proxy is simple and should be edited according to your needs. Possible values for the 'resolver' option are the first column in the list of public DNSCrypt resolvers.

DNS service for resolving queries. You can't add more than one resolver.

resolvers_list

string

no

/usr/share/dnscrypt-proxy/dnscrypt-resolvers.csv

Location of CSV file containing list of resolvers. When you use a custom DNSCrypt server and you later get problems when executing DNSCrypt, have a look in the resolver list (/usr/share/dnscrypt-proxy/dnscrypt-resolvers.csv) and make sure the resolver you chose is listed there. If not you may need to manually add it or just update the resolver list with the official one. Make sure to verify the integrity of the file before overwriting the local list!

ephemeral_keys

boolean

no

0

Improve privacy by using an ephemeral public key for each query. Note that you cannot yet use it with current versions of OpenWrt as the dnscrypt-proxy package is outdated and uses a version of DNSCrypt, which does not support ephemeral keys. Ephemeral keys option requires extra CPU cycles (especially on non-x86 platforms) and can cause huge system load. Disable it in case of performance problems. Also this option is useless with most DNSCrypt servers (all the servers using short TTLs for the certificates, which is done by default in the Docker image).

This options are only supported by Trunk:

Name

Type

Required

Default

Description

client_key

string

no

none

Use a client public key for identification. By default, the client uses a randomized key pair in order to make tracking more difficult. This option does the opposite and uses a static key pair, so that DNS providers can offer premium services to queries signed with a known set of public keys. A client cannot decrypt the received responses without also knowing the secret key. The value for this property is the path to a file containing the secret key. The corresponding public key is computed automatically

syslog

boolean

no

1

Send logs to the syslog daemon

syslog_prefix

string

no

dnscrypt-proxy

Log entries can optionally be prefixed with a string

query_log_file

string

no

none

Log the received DNS queries to a file, so you can watch in real-time what is happening on the network. The value for this parameter is a full path to the log file. The file name can be prefixed with ltsv: in order to store logs using the LTSV format (ex: ltsv:/tmp/dns-queries.log)

Blacklists allow you to block domains, ip, … see https://github.com/jedisct1/dnscrypt-proxy/wiki/Filtering. The value for this property is the blocklist type and path to file (ex: domains:/path/to/domains-blacklist-file.txt or ips:/path/to/ips-blacklist-file.txt). You can specify several blocklists by adding several list blacklist options.

If you need to specify other options, you will have to edit the /etc/init.d/dnscrypt-proxy script.

Note: I've had a little bit of confusion at setup, so I want to remind you; address and port strings are for local proxy server, you just have to pick a DNSCrypt server from the resolvers list, put its name in resolver string and comment out resolvers and resolvers list settings.

Now we will start DNSCrypt and enable auto boot for it:

/etc/init.d/dnscrypt-proxy enable
/etc/init.d/dnscrypt-proxy start

Note: If dnscrypt-proxy is not starting after a router reboot, it may be trying to start before the network interface is fully up. Add the following to /etc/rc.local, above the line "exit 0":

sleep 10
/etc/init.d/dnscrypt-proxy start

dnsmasq

Assuming you are using dnsmasq, edit the bold lines in /etc/config/dhcp

We have disabled /tmp/resolv.conf.auto file since it instruct dnsmasq to use your ISP's DNS.

noresolv option also disables /etc/resolv.conf file for similar reason.

127.0.0.1#5353 is the DNSCrypt address.

/pool.ntp.org/208.67.222.222 adds an exception for pool.ntp.org, which will be resolved through the standard unencrypted DNS channel. DNSCrypt requires precise time, otherwise it will not resolve any domain, including pool.ntp.org. So if your device's time was incorrect, it could never update its time, and therefore DNSCrypt would never work. So we set this exception so that pool.ntp.org queries will always bypass DNSCrypt and resolve with the standard unencrypted OpenDNS method.

Reboot router or restart dnsmasq for the changes to take effect.

/etc/init.d/dnsmasq restart

Multiple DNSCrypt instances

This option is not available in Chaos Calmer and earlier

Multiple DNSCrypt instances is helpful to provide dnsmasq with a fallback nameserver without losing the privacy benefits of DNSCrypt (source).

Add more resolver entries to your /etc/config/dnscrypt-proxy configuration (note that each resolver must be on a different port):